The present invention relates to image formation devices such as facsimile machines, printers and copiers.
Various types of image formation devices (facsimile machines, printers, copiers, etc.), forming images on print media (paper, OHP sheets, labels, etc.), are in wide use today. For the image formation devices, techniques for forming images using a ribbon coated with ink have long been well known. In such techniques, removal of slack occurring to the ribbon from various causes is one of serious challenges.
A technique for removing the slack of the ribbon has been employed for an image formation device including a recording head driving unit (for driving and switching a recording head between a head-up state and a head-down state) and an ink ribbon feeding unit (for feeding an ink ribbon of an ink ribbon cassette) both mounted on a carriage (which can hold the ink ribbon cassette) and being capable of driving both the recording head driving unit and the ink ribbon feeding unit with a single driving source. In the technique, the slack of the ink ribbon is removed by feeding the ink ribbon after the recording head is moved up (in the head-up state) in addition to the feeding of the ink ribbon in the head-down state (see Japanese Patent Provisional Publication No. HEI10-226130, for example).
Even in image formation devices having no function of moving the recording head up/down, the slack occurs to the ribbon when the ribbon is replaced, for example. In image formation devices of a well known type, the ribbon is stored in a ribbon cassette having two spools, and ink on the ribbon is transferred to a recording medium (paper, etc.) fed between the recording head and a platen while the ribbon is pulled out from one spool and rolled up by the other spool. In such image formation devices, the slack tends to occur when the ribbon cassette is attached and detached to/from the image formation device.
It is possible to apply the above-described technique to the image formation devices of the above type to remove the slack of the ribbon. Specifically, after the ribbon cassette is set to the image formation device, the slack of the ribbon can be removed by separating the recording head and the platen from each other and rolling up the ribbon.
However, in order to realize the method, a mechanism for separating the recording head and the platen from each other has to be installed in the image formation device, which substantially adds to the complexity of the device. Providing the image formation device with such a separating mechanism (which is originally unnecessary) in order to remove the slack of the ribbon is not a realistic approach in terms of reducing the size and cost of the device.
In another known method for removing the slack of the ribbon in an image formation device having no function of moving the recording head up/down, when an upper cover of the image formation device is closed, the platen roller is driven (rotated) while the driving force is transmitted also to a ribbon roll-up part so as to drive both the platen roller and the ribbon roll-up part and thereby remove the slack of the ribbon (see U.S. Pat. No. 4,527,172 (hereinafter referred to as “the '172 patent”), for example).
While the method of the '172 patent is capable of removing the slack of the ribbon, the method of rotating both the ribbon roll-up part and the platen for the removal of the slack, causes the ribbon roll-up to increase in length and an increased amount of ribbon to be wasted without being used for image formation.
Specifically, in the image formation device configured as above, the platen roller is rotated at a constant speed for image formation and a roll-up speed of the ribbon roll-up part is generally set higher than a feeding speed of the platen roller in consideration of a gradual increase of a roll-up diameter of the ribbon roll-up part as the ribbon is rolled up. The slack of the ribbon is removed by driving the platen roller (facing the recording head) and the ribbon roll-up part of the ribbon cassette, that is, by operating the platen roller and the ribbon roll-up part in the same way as in the image formation.
Consequently, the rotation of the ribbon roll-up part for the removal of the slack is necessarily accompanied by rotation of the platen roller, and a new part of the ribbon is necessarily pulled out and supplied by the platen roller resulting in a large amount of new ribbon being wasted.